Hard decsision. I'd probably rule out the Velodyne, doesn't go as low or loud. The HSU is ported, giving you close to flat frequency responses to 25 hertz and nothing at all after that, obviously your room will effect the frequencies the most. The 10" Dayton is sealed, this will give you an F3 in the mid to upper 30's, but since it's sealed the roll-off is much more gradual, so you will have decent output to 20 hertz, although it will not go as loud (about 3 dB less) as the HSU. Now in my opinion, the Adire Rava offers much more for your money, it offers a more powerful amp, a bigger 12" driver, and a slightly larger enclosure, this will go lower and louder than the Dayton, and will have an F3 in the mid to upper 20's, and since it's sealed you'll have plenty of output at 20 hertz. All of these subs will pretty much go just as loud, varying a couple dB, but you wouldn't even notice. Plus the Rava is only $400. www.adireaudio.com . If you absolutely can't have a bigger sub, I'd go with the Dayton only cause it's sealed and I prefer the roll-off and punchy sound of sealed.

-Joey